The present invention relates to controlling brown stain in wood, and more particularly, this invention relates to the use of a combination of chlorothalonil and methylene bis-thiocyanate to control brown stain.
Typically, white pine (Pinus strobus), ponderosa pine, or western hemlock wood develops a brown stain, also known as coffee stain, on its surface due to oxidation during kiln drying. These stains greatly reduce the marketability of the lumber and necessitate downgrading the wood. The staining is most likely to occur when fresh, unseasoned lumber is stacked and stored for several days during warm or humid weather prior to kiln drying. Kiln-brown stain is thought to result as an enzymatic reaction involving a peroxidase and subsequent oxidation or polymerization of a leuco product in a two-step chemical process. High kiln temperatures cause polymerization and oxidation that produce colored compounds (tannins and phlobotanins). Peroxidase activity on phenolic extractives is apparently accelerated at the moisture and oxygen levels that occur in freshly sawn boards during such periods.
Prior art methods of combatting such stains for conifers have included mild kiln schedules and using reducing agents or pH alteration on the freshly cut lumber. Formerly, dip application of sodium azide and sodium fluoride were found to prevent kiln-brown stain. However, these compounds are toxic, and safety concerns have largely limited there use. Ammoniacal zinc oxide and several alkali salts were also shown to provide some control. Phosphoric acid and several 8-hydroxyquinoline compounds are environmentally acceptable and have been shown to control brown stain in sugar pine under laboratory conditions. However, as the compounds are largely toxic, dangerous, and possibly explosive under certain conditions and further some are not regulated by EPA, the search for a suitable stain control continues.
U.S. Pat. No. 5,009,937 to West et al. teaches a control for another kind of wood stain, specifically a sapstain control composition consisting of an aqueous solution of chlorothalonil and sodium tetraborate decahydrate (borax) in an amount 3 to 9 times greater than the amount of chlorothalonil.
Japanese Patent No. 04/069393 teaches a composition to control fungus which employs the combination of tetrachloro isophthalonitrile and at least one of methylenebisthiocyanate, 3-iodo-2-propynyl-n-butylcarbamate, or 2-methoxycarbonyl aminobenzimidazole.
Accordingly, there is a need for controlling brown stain, effectively using environmentally safe means. Further, there is a need for a superior system for the control of brown stain.